Secretory Leukocyte Protease Inhibitor (SLPI) was first discovered as an 11.7 kD inhibitor for elastase and cathepsin G (Thompson et al., Proc Natl Acad Sci USA 1986; 83:6692-6). SLPI is expressed by mast cells (Westin et al., Biol Chem 1999; 380:489-93) and is present in the mucosa of the upper airway (Fryksmark et al., Ann Otol Rhinol Laryngol 1982; 91:268-71) and sputum (Kramps et al., J Histochem Cytochem 1981; 29:712-9). High amounts of SLPI have been measured in the nasal (Lee et al., Am Rev Respir Dis 1993; 147:710-6), trachea and broncus (Kramps et al., Am Rev Respir Dis 1984; 129:959-63; Mooren et al., J Histochem Cytochem 1982; 30:1130-4), maxillary sinus (Fryksmark et al., supra) and goblet cells of the bronchiole epithelium (Willems et al., Am Rev Respir Dis 1989; 139:1244-50).
The crystallography studies of SLPI have shown the molecule to be a member of the Whey Acidic protein-like family (Grutter et al., Embo J 1988; 7:345-51). These proteins have two 4 disulfide linked domains. The 4 disulfide linkages and helical structure of each domain make SLPI a very stable protein. Bovine (Grutter supra) and sheep (Pemberton et al., Biochim Biophys Acta 1998; 1379:29-34) mast cell proteases have been shown to cleave SLPI at Leu72-Met73. Others have shown a lower molecular weight processed product of SLPI but have not characterized the enzyme responsible for this cleavage (Ota et al., Hum Reprod 2002; 17:2517-22). SLPI was described as the most effective inhibitor for chymase (Walter et al., Arch Biochem Biophys 1996; 327:81-8; and Fink et al., Biol Chem Hoppe Seyler 1986; 367:567-71).
Chymase is a chymotryptic serine proteinase that belongs to the peptidase family S1. It is expressed in mast cells and globule leucocytes of skin and lung and thought to function in the degradation of the extracellular matrix, the regulation of submucosal gland secretion, and the generation of vasoactive peptides. It has a maximal activity immediately upon release into the extracellular matrix after mast cells have been activated (Takai et al., FEBS Lett 467: 141-144, 2000). There are two forms of mammalian chymase, α and β, which differ in species and have different functions. In human and baboons, only α-chymase is found, while dogs, rats, and mice have both α- and β-chymases (Dell'Italia et al., Curr Opin Cardiol 2003 17: 374-379).
Although the precise patho-physiological roles of chymase have yet to be determined, chymase has been implicated in microvascular leakage, neutrophil accumulation, the stimulation of mucus secretion, and the modulation of cytokines, etc. A potent, chymase-selective inhibitor may be indicated in mast cell-mediated diseases such as asthma, pulmonary inflammation, and chronic obstructive pulmonary diseases (COPD). Because chymase can play a role in the generation of cardiac and vascular wall angiotensin II, a chymase inhibitor may have potential use as an antihypertensive treatment for vascular wall injury and inflammation (atherosclerosis/restenosis), as well as cardiac hypertrophy. Chymase is a target for cardiovascular disease therapies (Doggrell et al., Can J Physiol Pharmacol. 2005 February; 83(2):123-30). In addition, chymase has also been proposed to play a critical role in diseases such as rheumatoid arthritis (Kobayashi et al., Jpn J Pharmacol. 2002 September; 90(1):7-11), diabetic nephropathy (Huang et al., J Am Soc Nephrol. 2003 July; 14(7):1738-47), and inflammatory diseases (Muto et al., Idrugs., 2002, 12, 1141-50)
Therefore, compounds designed to inhibit the biological activity of chymase may offer therapeutic benefit in a number of disease areas. Selective chymase inhibitors have been developed, which include TY-51076, SUN-C8257, BCEAB, NK320, and TEI-E548 (see Doggrell et al supra). Promising results have been obtained with these chymase inhibitors in animal models of myocardial infarction, cardiomyopathy, and tachycardia-induced heart failure. To facilitate the test of chymase inhibitors in human, as well as the study of chymase activity in human in general, there is a need to develop a biomarker for chymase activity in human.